A rectangular cake is transported via a truck to a restaurant. On the way to the destination, the truck
hits a pothole, which shatters the cake in
At the destination, the damage is assessed, and the customer decides to order a replacement cake
of the same dimensions. Unfortunately, the original order form was incompletely filled and only the
width
Input Specification
The input consists of the following integers:
- on the first line, the width
of the cake; - on the second line, the number
of shattered pieces; - on each of the next
lines, the width and length of each piece.
Constraints
For each
Output Specification
The output should be the integer
Sample Input
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4
7
2 3
1 4
1 2
1 2
2 2
2 2
2 1
Sample Output
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6
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